### Overview
Stockfish is a free UCI chess engine derived from Glaurung 2.1. It is
not a complete chess program and requires some UCI-compatible GUI
(e.g. XBoard with PolyGlot, eboard, Arena, Sigma Chess, Shredder, Chess
Partner or Fritz) in order to be used comfortably. Read the
documentation for your GUI of choice for information about how to use
Stockfish with it.
This version of Stockfish supports up to 64 CPUs. The engine defaults
to one search thread, so it is therefore recommended to inspect the value of
the *Threads* UCI parameter, and to make sure it equals the number of CPU
cores on your computer.
### Files
This distribution of Stockfish consists of the following files:
* Readme.md, the file you are currently reading.
* Copying.txt, a text file containing the GNU General Public License.
* src, a subdirectory containing the full source code, including a Makefile
that can be used to compile Stockfish on Unix-like systems. For further
information about how to compile Stockfish yourself read section below.
* polyglot.ini, for using Stockfish with Fabien Letouzey's PolyGlot
adapter.
### Opening books
This version of Stockfish has support for PolyGlot opening books. For
information about how to create such books, consult the PolyGlot
documentation. The book file can be selected by setting the *Book File*
UCI parameter.
### Compiling it yourself
On Unix-like systems, it should be possible to compile Stockfish
directly from the source code with the included Makefile.
Stockfish has support for 32 or 64-bit CPUs, the hardware POPCNT
instruction, big-endian machines such as Power PC, and other platforms.
In general it is recommended to run `make help` to see a list of make
targets with corresponding descriptions. When not using the Makefile to
compile (for instance with Microsoft MSVC) you need to manually
set/unset some switches in the compiler command line; see file *types.h*
for a quick reference.
### Terms of use
Stockfish is free, and distributed under the **GNU General Public License**
(GPL). Essentially, this means that you are free to do almost exactly
what you want with the program, including distributing it among your
friends, making it available for download from your web site, selling
it (either by itself or as part of some bigger software package), or
using it as the starting point for a software project of your own.
The only real limitation is that whenever you distribute Stockfish in
some way, you must always include the full source code, or a pointer
to where the source code can be found. If you make any changes to the
source code, these changes must also be made available under the GPL.
For full details, read the copy of the GPL found in the file named
*Copying.txt*